Polyamide based antibacterial powder paint composition

ABSTRACT

Antibacterial powder paint composition consisting mainly of polyamide, characterized in that zinc and/or silver/zinc composite compound is incorporated in polyamide as antibacterial agent. This powder coating composition can produce a film with improved antibacterial activity, discoloration and endurance.

FIELD OF TECHNOLOGY

This invention relates to polyamide-type antibacterial powder paintcomposition.

An objective of this invention is to provide a polyamide-typeantibacterial powder paint composition improved in discoloration.

PRIOR ARTS

Surface coating is well-known and has been used since old days toprotect-metallic materials from rust and to improve appearance andproperties Of various materials. Organic coating materials such as estertype, epoxy type and combination thereof, urethane type, acryl type,polyamide type and fluorine type resins are used widely. These organiccoating materials are usually dissolved or dispersed in organic solventto facilitate handling and processing. Use of organic solvent, however,is not desirable from the view point of contamination in surrounding andin working environment and hence is controlled by law. To solve thisproblem, water-soluble paints, water-dispersion paints and powder paintare developed as solvent-free paints and are used in practical uses.

Anti-bacterium and anti-mold property are, also required when the paintsare used in such applications that coated products are contacted withunspecified number of men and in the field of foods, medical care andsanitation such as shopping carts, handles of bass and trains,kitchenware and bathroom wears. In these applications, it is commonpractice to add or incorporate antibacterial agent or fungicides inmaterial resins.

A variety of anti-bacterium and fungicides are known. Naturalanti-bacterium and fungicides are difficult to handle because theypossess relatively low boiling points. Organic anti-bacterium andfungicides have a problem of low heat-stability so that their efficiencyis lost during melting stage, although they are compatible with resins.Inorganic anti-bacterium and fungicides possess high heat-stability buthave such problems as poor solubility in resins and low durability dueto dissolution into water.

Therefore, it is critical to select anti-bacterium and fungicides inaccordance with natures of resin to be combined, molding conditions, usecondition, applications or the like.

PROBLEMS TO BE SOLVED BY THE INVENTION

Inorganic antibacterial agent, in particular silver type antibacterialagent has a problem of discoloration when the agent is used withpolyamide type powder paint and hence its application is restricted.

An object of this invention is to provide such antibacterial compositionthat shows little problem of discoloration in polyamide type powderpaint.

Inventors found that the objective can be realized by incorporating aspecial antibacterial agent in the resin.

Means to Solve the Problems

This invention provides antibacterial powder paint compositionconsisting mainly of polyamide, characterized in that zinc and/orsilver/zinc composite compound is incorporated in polyamide as anantibacterial agent.

Embodiment

“Polyamide” in this invention is understood as polyamide which is apolymer of amino carboxylic acid having a carbon number of 6 or more orof lactam or a polymer of diamine having a carbon number of 6 or moreand salt of dicarboxylic acid, for example, aminocarboxylic acid such asω-aminocaproic acid, ω-amino enanthic acid, ω-amino caplyric acid,ω-amino pelargonic acid, ω-amino capric acid, ω-amino undecanoic acid,and ω-amino dodecanoic acid; lactam such as caprolactam, enantlactam,caprillactam and laurolactam; salts such ashexamethylenediamine-adipate, hexamethylenediamine-sebacate,hexamethylenediamine-isophthalate, undeca methylenediamine-adipate and4,4′-diaminodichlorohexylmethane-dodecanoate. Polyamide can behomopolymer or copolymer and can be blended with other resins. Polyamidecan also contain catalyst and various stabilizers. Preferably, polyamide11 and polyamide 12 are used.

“Powder paint” used in this invention is understood as a productprepared by mixing a variety of additives such as pigment, dye,heat-stabilizer, light-stabilizer, lubricant, plasticizer, antistaticagent, crystal nucleus forming agent and fire retardant with the“polyamide” resin in powder forms or by melt-mixing them followed bypulverization. The paint is applicable to any coating techniqueincluding fluidized bed coating, electrostatic coating and melt-spraycoating.

“Antibacterial agent” used in this invention can be mentioned as naturalproducts (for example, hinokitiol, chitin, chitosan), organic compounds(for example, imidazole, thiazole, nitrile, haloalkylthio, pyridine,triazine, brom type, quaternary ammonium type) and inorganic compounds(for example zeolite, zirconium phosphate, calcium phosphate, titaniatype, silicon oxide, inorganic ion exchanger).

In this invention, the antibacterial agent must be zinc and/orsilver/zinc complex compound. These metals may be supported on zeolite,inorganic ion exchanger or inorganic glass compound for example.

The composition containing Zn and/or Ag/Zn compound according to thepresent invention can have any form such as a composition on which allcomponents are mixed mechanically in powder form, a composition in whichantibacterial agent deposit on a surface qf polyamide powder, acomposition in which antibacterial agent is coated on a surface ofpolyamide powder, a composition in which antibacterial agent is kneadedin polyamide.

The proportion of the antibacterial agent in the composition is notspecially limited but is decided so as to balance efficiency and price.Usually, the proportion of the antibacterial agent in the composition ishigher than 0.01% but lower than 10%, preferably higher than 0.05% butlower than 5%, more preferably higher than 0.1% but lower than 3%.

The composition containing antibacterial agent according to the presentinvention can be prepared by any known technique. For example,antibacterial agent and polyamide powder are mixed mechanically toprepare the composition. Or, polyamide powder and antibacterial agentare mixed firstly and then antibacterial agent is coated or deposited ona surface of the polyamide particle by means of collision energy orshear energy for example to prepare the composition. Or, antibacterialagent is kneaded in polyamide and then the kneaded product is pulverizedinto a fine particles of composition. These techniques are only forillustration the present invention is not limited to these methods.

Powder coating method of polyamide powder composition containing theantibacterial agent is not limited specially but can be any known methodincluding fluidized bed method, electrostatic coating and melt-spraying.

Function

The composition according to the present invention gives anti-microbialproperty to powder paint and gives good surface characteristic withlittle or no discoloration during heating stage in a coating process.

Such advantage of the present invention is desired and effective in suchapplications as grab handles of public vehicles, shopping carts, dishwasher, kitchenware and wall materials used in humid rooms.

EXAMPLE

The present invention will be explained in much in details by followingExamples but the present invention should not be limited to theexamples.

In Example and Comparative Example, the qualities of coating and coatedfilm were determined by following methods.

(1) Coating

Epoxy type primer was sprayed on a surface of a de-rust and degreasediron plate having a thickness of 3.2 mm and then coating was effected insuch a manner that a dried film had a thickness of 10 micron. Theresulting coated iron plate was heated in an oven at 400° C. for 3minutes 40 seconds and then was taken out when the surface temperatureof the iron plate became 280° C. The resulting heated plate was immersedin a fluidized bed filled with a powder paint containing antibacterialagent to obtain a test sample having a coated film having a thickness of400 microns.

(2) Anti-microbial Property of the Coated Film

Test bacterium (Bacillus coli and yellow grapes Staphylococcus aureus)as cultivated in NA culture medium with 37° C. for 24 hours. 0.15 ml ofthe bacterium liquid prepared was dropped onto a surface of the testsample film (above-mentioned, 3 cm×3 cm) and a polyethylene film was puton the surface. Assembly was left at 35° C. under a relative humidity of90%. Test was repeated for three times for one sample. The sameprocedure as above was repeated on polyethylene film as control.

After the sample was left for 24 hours, the plate was washed with 2 mlof physiological salt solution to collect survived bacterium. Thisliquid was cultured by Agar Plate Culture technique (cultured at 35° C.for 2 days) to determine a number of survived bacterium.

(3) Adhesion of Coated Film to Iron Plate

Test according to JIS K5400, 8.5.2 (Japanese Industrial Standard). Unitarea had an interval of 2 mm. The results were expressed by a number ofunit areas left (not-peeled off). 25/25 means that “there was no unitarea peeled off”.

(4) Hue, Whiteness and Gloss of Coated Film

-   Hue: determined according to JIS K5400, 7.4.2.-   Whiteness: WI was determined according to ASTM E313.-   Gloss: determined according to JIS K5400, 8.5.2 at angle of    incidence of 60°.    (5) Durability of Coated Film-   Durability: determined after coated iron plate was hung in water    23° C. for predetermined time duration-   Accelerated weather-resistance: determined according to JIS K5400,    7.6.

Example 1, 2, Comparative Example 1, 2

Following antibacterial agents were mixed to a powder paint (RILSAN®fine powder product of Elf Atochem) W1482 consisting mainly of polyamide11 in Henschel mixer to prepare respective powder paint compositions:

-   1) Silver-substituted inorganic ion exchanger (antibacterial agent    A),-   2) Zinc type inorganic glass (antibacterial agent B) and-   3) the zinc type inorganic glass was combined with the    silver-substituted inorganic ion exchanger (antibacterial agent C)

The resulting powder paint composition was coated on iron plate in afluidized bed.

The whiteness of a film containing no antibacterial agent(composition 1) was 76.8 (Comparative Example 1), and the whiteness of afilm containing 0.2% of the antibacterial agent A (composition 2) was54.5 (Comparative Example 2). This shows that the antibacterial agent Acaused sever discoloration.

On the contrary, the whiteness of a film containing 0.2% of theantibacterial agent B (composition 3) was 76.0 (Example 1), and thewhiteness of a film containing 0.2% of the antibacterial agent C(composition 3) was 75.9 (Example 2). In other words, these compositions3 and 4 showed no substantial difference in whiteness from thecomposition 1 containing no antibacterial agent.

Coated films obtained from the compositions 1 and 4 showed the sameadhesion of 25/25. This means that the antibacterial agent C did notdeteriorate adhesion.

The number of survived bacterium count in the composition 1 (containingno antibacterial agent) was 10E6 for Bacillus coli and 10E5 for yellowgrapes Staphylococcus aureus, while respective numbers of survivedbacterium count in the composition 2 (containing silver typeantibacterial agent), composition 3 (containing zinc type antibacterialagent) and composition 4 (containing silver/zinc composite antibacterialagent) were all under 10.

Example 3, Comparative Example 3

Into a powder paint (RILSAN® fine powder product of Elf Atochem) Gray3362 consisting mainly of polyamide 11, 0.3% of the compositeantibacterial agent consisting of zinc type inorganic glass andsilver-substituted inorganic ion exchanger (antibacterial agent C) wasmixed in Henschel mixer to prepare a powder paint composition(composition 5).

For comparison, a blank composition containing no antibacterial agent(Comparative Example 3) was also prepared.

The powder paint composition was coated on iron plate in a fluidized bedand the resulting film was subjected the accelerated weather-resistancetest effected under Sunshine Weather-meter for 1,000 hours. Bothcompositions showed the same color-difference (ΔE) of 0.8.

The gloss of film obtained from the composition 6 was 67.4, while thegloss of Comparative Example 3 was 64.0. This reveals such a fact thataddition of the antibacterial agent give little influence to gloss.

Example 4, Comparative Example 4, 5

Into a powder paint (RILSAN® fine powder product of Elf Atochem) W1482consisting mainly of polyamide 11, 0.5% of the composite antibacterialagent consisting of zinc type inorganic glass and silver-substitutedinorganic ion exchanger (antibacterial agent C) was mixed in Henschelmixer to prepare a powder paint composition (composition 6) and thepowder paint composition was coated on iron plate in a fluidized bed.The whiteness of the film (Example 4) was 76.5 which was not sodifferent from the value of 76.8 obtained in Comparative Example 1.

For comparison, a composition containing 0.5% of the antibacterial agentA (silver-type) (Comparative Example 4) was also prepared. The whitenessof this film was 41.2. This means that the discoloration was worse thanComparative Example 2.

Coated film of the composition 6 together with a coated film containingno antibacterial agent (Composition 1) was immersed in water 23° C. for1,000 hours. Difference * in the number of survived bacterium (increaseand decrease) after the treatment was 5 for Bacillus coli and 2 foryellow grapes Staphylococcus aureus. This reveals that the filmaccording to the present invention possesses high antibacterial. [*Difference in the number of survived bacterium was expressed by alogarithm of an inverse number of a ratio of a number of bacterium in afilm containing the antibacterial agent to a number of bacterium in afilm containing no antibacterial agent. Therefore, higher value showshigher efficiency].

Advantages of the Invention

As explained, the composition according to this invention givesantibacterial film which is hardly discolored during heating stage andhas enough endurance.

1. An article comprising: an object, and a coating on the object,wherein the coating comprises an antibacterial powder paint composition,comprising: a polyamide, and an antibacterial agent of zinc and/or asilver/zinc composite.
 2. An article according to claim 1, wherein thepolyamide is polyamide-11 or polyamide-12.
 3. An article according toclaim 1, wherein the polyamide is a powder and mechanically mixed withthe antibacterial agent.
 4. An antibacterial powder paint composition,comprising: a polyamide, and an antibacterial agent of zinc and/or asilver/zinc composite, wherein the agent is deposited on a surface ofthe polyamide that is a powder.
 5. An antibacterial powder paintcomposition, comprising: a polyamide, and an antibacterial agent of zincand/or a silver/zinc composite, wherein the agent is coated on a surfaceof the polyamide that is a powder.
 6. An article according to claim 1,wherein the antibacterial agent is kneaded with the polyamide that is apowder.
 7. An article according to claim 1, further comprising a supportfor the zinc and/or silver/zinc composite.
 8. An article according toclaim 7, wherein the support is a zeolite, an inorganic ion exchanger,or an inorganic glass compound.
 9. An article according to claim 7,wherein the support is an inorganic ion exchanger or an inorganic glasscompound.
 10. A public vehicle handle, a shopping cart, a dishwasher, akitchenware or a wall material painted with an antibacterial powderpaint composition, comprising: a polyamide, and an antibacterial agentof zinc and/or silver/zinc composite.
 11. A public vehicle handle, ashopping cart, a dishwasher, a kitchenware or a wall material paintedwith a composition according to claim
 5. 12. An article according toclaim 1, wherein the polyamide is a powder.
 13. An article according toclaim 1, further comprising at least one additive of a pigment, a dye, aheat-stabilizer, a light-stabilizer, a lubricant, a plasticizer, anantistatic agent, a crystal nucleus forming agent, or a fire retardant.